Memory is often incorporated into integrated circuitry. The memory may be used, for example, in computer systems for storing data.
Memory may be fabricated as an array of individual memory cells, with each memory cell being configured to retain or store memory in at least two different selectable states. In a binary system, the storage conditions are considered as either a “0” or a “1”.
Integrated circuitry fabrication continues to strive to produce smaller and denser integrated circuits. There is a continuing effort to reduce the number of components in individual devices because such can reduce the size of finished constructions, and can simplify processing. The smallest and simplest memory cell will likely be comprised of two conductive electrodes having a programmable material received between them. Such simple memory cells are often referred to as cross-point memory cells, in that they occur at the cross-point of overlapping conductivity lines.
Suitable programmable materials have two or more selectable resistive states to enable storing of information by an individual memory cell. The reading of the cell comprises determination of which of the states the programmable material is in, and the writing of information to the cell comprises placing the programmable material in a predetermined resistive state. If a memory cell has two selectable states, it is known as a single level cell. Memory cells that have four or more selectable memory states are known as multi-level cells.
Programmable materials that are receiving increasing interest are variable resistance memory materials, such as phase change materials which reversibly change from crystalline states to amorphous states with the application of current. The crystalline and amorphous states differ from one another in resistivity. Thus, data bits may be stored in the phase change materials as the phase of the material, with the phase of the material having relatively high resistivity being one type of data bit (either a “1” or a “0” in a single level cell), and the phase of the material having relatively low resistivity being another type of data bit. Variable resistance memory materials may be used in multi-level cells, as well as within single level cells.
Example phase change materials are chalcogenides, such as, for example Ge2Sb2Te5.
Although cross-point memory cells show promise for utilization in integrated memory architectures, there remain challenges in constructing and utilizing such memory cells.